The Molecular Architecture of the Chloroplast Thylakoid Membrane. Mapping of protein complexes in different structural domains and effect of light induced protein phosphorylation on domain composition

Abstract: Non-detergent procedure for isolation of sub-thylakoid vesicle populations derived from different structural domains of the chloroplast thylakoid membrane has been developed. Sub-thylakoid vesicles representing the grana, grana core, stroma lamellae and the grana margins have been isolated and their protein composition has been investigated. Furthermore a novel non-detergent procedure for investigating the pigment composition of photosynthetic complexes located in the different structural domains has been developed. This procedure circumvents selective extractions and pertubing effects often combined with detergent isolations of membrane bound protein complexes. The fractionation experiments show that the NADPH dehydrogenase, suggested to be operating as NADPH or ferredoxin-plastoquinone oxidoreductase in cyclic electron transport around photosystem I, is stoichiometrically depleated on photosystem I basis in the grana domain. The fractionation studies are consistent with the model of the thylakoid membrane where the photosystems in the grana are operating in a linear electron transport whereas the site of cyclic electron transport is in the stroma lamellae. It is suggested that partial destacking of grana, as a result of light induced protein phosphorylation, may promote the exposure of the granal photosystem I centers to the chloroplast stroma and thereby enhance their participation in cyclic electron transport activity.